Fungal glucoamylase preparations, particularly those derived from members of the Aspergillus and the Rhizopus genera are known to convert starchy materials to substantial amounts of dextrose. In addition, certain fungi capable of producing glucoamylase under suitable fermentation conditions also produce acid fungal protease. The acid fungal protease co-produced is potentially useful in the food, brewing and photographic industries. Thus, this protease can be used in the preparation of protein hydrolysates at low pH values (soy sauce), preparation of orange juice concentrate (peeling the skin), prevention of chill haze in beer (as a potential replacement for papain) and as a digestive aid in animal feed (chicks, piglets, etc.).
Acid fungal proteases have been isolated from the culture filtrates of Aspergillus niger, Aspergillus saitoi, Aspergillus oryzae and Aspergillus niger var. macrosphorus and Rhizopus species.
It is, of course, desirable to separate the glucoamylase from the acid fungal protease produced during the fermentation of these organisms both to purify the glucoamylase and to provide a useful byproduct of the fermentation.
In the prior art, for example, Tomonaga reports in J. Gen. Appl. Microbiol., 12, 267 (1966) that acid protease is precipitated using certain salts and recovered by ion-exchange chromatography. More specifically, the enzyme was fractionated using DEAE-cellulose and SE-sephadex column chromatography at pH 4.1 using the procedures disclosed by Tomonaga, et at, J. Gen. Appl. Microbiol, 10, 373 (1964) and Ichishima, et al, Biochem. Biophys. Acta, 99, 360 (1965).
We have discovered that at a certain pH range, the acid fungal protease is associated with the fungal mycelium, i.e. biomass, in the fermentation broth and it is an object of this invention to provide a simple method for the recovery in good yields of acid fungal protease from the fungal mycelium.